Activation of the gonadotropin-releasing hormone (GnRH) receptor initiates a number of complex signaling cascades in pituitary gonadotropes. The rhythmic stimulation of gonadotropes by pulsatile GnRH underlies the differential control of luteinizing hormone and follicle-stimulating hormone production, and ultimately the control of reproduction. GnRH receptor signaling cascades regulate gonadotropin secretion, gene transcription and cell differentiation. We have shown that GnRH regulates protein synthesis and activates the unfolded protein response (UPR), a protective response to modulate stressful demands of protein synthesis. The UPR also activated by inflammatory and metabolic stress signals. The regulatory schemes utilized by the GnRH receptor are essential to maintain cell homeostasis and sensitivity to recurring GnRH pulses. To maintain pulse sensitivity and hormone synthesis, gonadotropes must resolve the intracellular alterations induced by secretion, increase protein synthesis to continue to meet these demands, and resolve the signaling events activated by the previous pulse to allow full response to the next. We have identified the UPR and control of translation as central elements maintaining gonadotrope sensitivity to GnRH and biosynthetic capacity. We propose to examine these components in vitro to determine their mechanism of regulation and in experimental mouse models to determine their physiological role in reproduction. The UPR may provide a direct link between physiological stress and reproductive function. Specific Aim 1: The Unfolded Protein Response in gonadotrope function. We will determine the role of the three main regulators of the unfolded protein response, EIF2AK3 and ERN1, in normal gonadotrope cell function Specific Aim 2: Mechanisms of mRNA redistribution in response to GnRH We have demonstrated that GnRH causes a redistribution of mRNA in gonadotropes. We will determine the specificity of redistribution and the factors determining susceptibility to redistribution. Specific Aim 3: Physiological consequences of an impaired stress response in mice We will examine the role of the unfolded protein response in normal gonadotrope cell function by examining the reproductive impact of pituitary-specific knockout of critical UPR regulatory factors. PUBLIC HEALTH RELEVANCE: To preserve normal reproductive hormone production and to respond correctly to environmental cues, pituitary cells must minimize cellular stress and adapt to the demand of continued hormone production. We are investigating the mechanisms cells use to adapt to stress and preserve normal cell function. These regulatory pathways are essential to assure proper reproductive hormone synthesis and reproductive success.